DEVICE FOR PRODUCING COLD AT TEMPERATURE LOWER THAN THAT OF lambda -POINT OF HELIUM

ABSTRACT

A device for cooling to temperatures lower than that of the lambda -point of helium, in which some high-pressure helium, after being cooled, expands to low-pressure and flows back to the compression device, and the remainder of the He is cooled to below its lambda -temperature forming superfluid He4 that flows through a superleak, and normal He4, and a vortex tube for communicating.

United States Patent 1 I11 3,713,305 Staas et al. [4 1 Jan. 30, 1973 U4]DEVICE FOR PRODUCING COLD AT 3,427,817 2/l969 Rietdijk ..62/so0TEMPERATURE LOWER THAN THAT 3,447,339 6/1969 Rietdikj OF A-POINT 0EHELIUM 3,464,230 9/1969 Rietdijk .;....62/5l4 [75] Inventors: FransAdrianus Staas; Adrianus Petrus Severijns, both of EmmasinprimaryExamine, Meyer m, gel, Eindhoven, Netherlands Aomey Frank Trifari [73]Assignee: U.S. Philips Corporation, New

York, N.Y. 221 Filed: Dec. 16, 1969 [57] ABSTRACT A device for coolin totern eratures lower than that l 8 42 8 P [2 1 App] No of the A-point ofhelium, in which some high-pressure helium, after being cooled, expandsto low-pressure [52] :J.S.C|l "62/5292, 62/1514 and flows back to thecompression device and the remainder of the- He is cooled to below itsA-temperae 0 ea c ture forming superfluid He that flows through a su-[56] Reerences Cited perleak, and normal He, and a vortex tube forcommunlcatmg.

UNITED STATES PATENTS V M is H .6 3,360,955 l/l968 Witter ..62/5 l4 15Claims, 4 Drawing Figures mm 30 m;

SHEETIOFZ 'FRANS ANT mm m 3.713.305

, sum 2 0r 2 'INVENTORS FRANS A. sTAAs ADRIANUS P. savsmms MKW DEVICEFOR PRODUCING COLD AT TEMPERATURE LOWER THAN TI-IAT OF k-POINT OFIIELIUM BACKGROUND OF THE INVENTION The invention relates to a devicefor producing cold at temperatures lower than that of the A -point ofhelium. The device comprises a source for high pressure helium whichcommunicates with a supply system including a pre-cooler acounter-current heat exchanger in which the high-pressure helium iscooled to below its inversion temperature associated with said pressure,and a throttle device in which the high-pressure helium expands; theexpanded helium then flows via an outlet system and the saidcounter-current heat exchanger, to a suction place for low-pressurehelium.

Devices of the above-mentioned type are known as Joule-Thompson coolingsystems. In these devices, high-pressure helium is cooled by pre-coolersand in counter-current heat exchangers to below the inversiontemperature associated with the said pressure, and is then expanded in athrottle valve, in which a temperature decrease occurs. The expandedhelium is then returned, via the said counter-current heat exchangers,to a compression plant. The temperature at which the cold is produceddepends upon the pressure which prevails after the throttle valve. Inorder to reach very low temperatures it is necessary to expand to verylow pressures. A pressure of 1 atm. after the throttle valve isnecessary for reaching a temperature of 4.2K; for 3.6"K a pressure of katmosphere after the throttle valve is required, while for reaching atemperature of 1.9K a pressure of 17 mm Hg after the throttle valve isrequired. For reaching even lower temperatures, even much lowerpressures after the throttle valve are necessary. For reaching saidextremely low pressures after the throttle valve, it is necessary forthe compressor to have a suction pressure which, as a result of theresistance to flow in the counter-current heat exchangers, will have tobe even lower, which means that the compressors become extremely bulky.In practice it is therefore substantially impossible to produce cold attemperatures lower than l.9K.

SUMMARY OF THE NEW INVENTION municates on its one side, via one or moreheat exchangers in which the helium cools to below the )t-t'emperatureof helium and at least one controllable throttle valve, with a firstplace of the system of supply or outlet ducts, and communicates on itsother side with a cold space, said space further communicating, via avortex tube, with a second place of the device, where a lower pressureprevails than at the said first place. A superleak should be understoodto mean within the scope of the present invention, a mass of a materialhaving the property that normal helium cannot pass said mass, andsuperfluid helium can pass said mass without moving vortices occurringduring the flow.

A vortex tube is to be understood to mean within the scope of thepresent invention, a duct having dimensions such that, in the prevailingoperating conditions, moving vortices occur in the superfluid whenliquid helium flows through said duct.

By communicating the superl'eak with the system at a place of higherpressure and communicating the vortex tube with a place of a lowerpressure, a differential pressure occurs across the series arrangementof superleak, cold store and vortex tube. In the first instance theoverall differential pressure will occur across the vortex tube, becauseno temperature difference prevails across the superleak yet, andconsequently no differential pressure either. Due to this differentialpres-v sure across the vortex tube, medium therein will start flowing tothe second place, the superfluid helium exceeding its critical velocity,and vortices occurring, as a result of which normal helium is alsotransported to the second place. This means a thermal transport from thecold store to the said second place, so that the temperature in the coldstore will decrease and a temperature difference will occur across thesuperleak. This temperature difference corresponds to a differentialpressure adjusting across the superleak. An equilibrium condition willbe adjusted in which the overall differential pressure is distributedbetween the superleak and the vortex tube. So in this manner it isreached that without any extra precautions of the Joule-Kelvin coolingsystem, cold is nevertheless supplied at a temperature which is lowerthan corresponds to the pressure which prevails after the throttledevice; The device according to the invention enables the production ofcold at temperatures which are lK or lower, without it being necessaryfor the compressors of the Joule-Kelvin system to be excessively large.

In order to obtain a suitable differential pressure across the seriesarrangement of superleak, cold space andvortex tube, in a favorableembodiment of the device according to the invention at least one of thesaid throttle devices is arranged between the said first and the saidsecond place. This means that the differential pressure which prevailsacross the relative throttle device also prevails across the seriesarrangement of superleak, cold space and vortex tube.

It is known from prior art of a Joule-Kelvin system in which cold isproduced at temperatures which are lower than the temperature whichcorresponds to' the pressure after the throttle device. This is achievedin' that the throttle device is constructed as a throttle ejector, theoutlet side of which communicates on the one side, via the saidcounter-current heat exchangers, with the suction side of thecompression device, said outlet side communicating on the other hand,via a throttle valve, with a cold space the vapor space of whichcommunicates with the suction side of the ejector. The suction pressureof the ejector will prevail in the cold space, so that the cold issupplied at a temperature which is lower than the temperature at theoutlet side of said ejector. Such a device operates excellently fortemperatures lying above that of the lt-point of helium, but when thetemperature at the outlet side of the ejector or in the cold space fallsconsiderably below that of the lt-point of helium, the fact presents.itself that in the duct communicating the cold space with the ejector,pressure gradients occur which cause thermal flows from the outlet sideof the ejector to the cold space, which is just not the intention in arefrigerator, and

consequently is disturbing to the operation of the refrigerator. Afurther embodiment of the device ac cording to the invention provides asolution to the said problem and is characterized in that at least oneof the said throttle devices is formed by a throttle ejector, the

outlet of said ejector communicating on the one side with the system ofoutlet ducts and communicating on the other hand, if desirable through acounter-current heat exchanger and a throttle valve, with aheatexchanging space the vapor space of.which communicates, via the saidcounter-current heat exchanger, with the suction side of the ejector,the superleak communicating with its one side, via a heat exchanger inwhich the helium exchanges heat with the heatexchanging space, athrottle value and, if desirable, a further heat exchanger, with afirstplace of the system of supply ducts situated in the direction of theflow in front of the throttle ejector, the vortex tube communicatingwith the heat-exchanging space.

In a further embodiment in which one of the throttle devices is alsoformed by a throttle ejector the outlet of said ejector communicates,beside with the heatexchanging space, also via a further throttle valveand a further heat exchanger in which the helium exchanges heat with theheat'exchanging store, with the one side.

of the superleak, the vortex tube furthermore communicating again withthe heat-exchanging space. In both latter casesv again a differentialpressure prevails across the series arrangement of superleak, cold spaceand vortex tube, as a result of which cold is produced in the cold spaceat temperatures which are lower than those which prevail in theheat-exchanging space.

The cold produced in the cold space may be used for cooling articles. Insuch cases it is frequently not possible, for all kinds of structuralreasons, to contact said articles directly with said space, so that thecold has to be supplied at some distance from the space. In order torealize this efficiency, a further embodiment is characterized in thatat least oneduct communicates with the cold space and with its otherside can be brought in thermal contact with the place to be cooled, ifdesirable via a further space, said duct comprising a sintered superleakwhich extends throughout the length of the duct and covers a part of thecross-section thereof. In this manner it is possible in a very efficientmanner to supply the produced cold at a distance from the cold store.

In connection with the checking of heat leak it is furthermore ofadvantage, according to the invention, to arrange the superleak againstthe inner wall of the duct.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may bereadily carried into effect, a few examples ofdevices as described abovewill now be described in greater detail with reference to theaccompanying drawings.

FIGS. 1, 2, 3 and 4 diagrammatically show not to scale four differentembodiments of devices for producing cold at temperatures lower thanthat of the A-point ofhelium. I a

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference numeral 1 in FIG, 1denotes a'compression device the outlet side 2 of which, for compressedhelium, communicates with a system of supply ducts 3, in which a watercooler 4 for removing the heat of compression, a number ofcounter-current heat exchangers 5, and two pre-coolers 6 and 7' arearranged. The system of supply ducts 3 communicates with the inlet 8 ofan ejector 9. The outlet side of said ejector communicates at 10 on theone hand with the system of outlet ducts 11 in which the counter-currentheat exchangers 5 are also incorporated, and on the other hand with aduct 12which communicates, via a counter-current heat exchanger 13having a low resistance to flow, on the one hand with a throttle valve14 and on the other hand with a throttle valve 15. Throttle valve 14opens into a heat-exchanging space 16 which communicates with thesuction side 17 of the ejector 9. The throttle valve 15 communicateswith a heat exchanger 18 which is in thermal contact with the space 16and in turn communicates with a superleak 19 which communicates with itsother side with a cold space 20. This cold space communicates, through avortex tube 21, with the heat exchanging space 16.

The operation of this device is as follows: the compressor l compresseshelium to a pressure of approximately 30 atm. which compressed heliumleaves the compression device via the outlet 2 and delivers its heat ofcompression to' cooling water in the heat exchanger 4. The compressedhelium then flows through the first counter-current heat exchanger 5 andthen along the precooler 6, then through the second heat exchanger 5,and then along the second pre-cooler 7, and then through the lastcounter-current heat exchanger Sin which the high-pressure helium willthen have a temperature which lies below the inversion'temperatureassociated with the pressure of 30 atm.

The'high-pressure helium'then expands in the ejector 9 to a pressure of,for example, I atm. and a temperature of 4.2K. A part of the expandedhelium flows via the outlet duct 11 to the inlet side 22 of thecompression device 1. Another part of the expanded helium flows via duct12 and heat exchanger 13 to the throttle valves .14 and 15. Since theheat-exchanging space 16 communicates with the suction side 17 of theejector 9, a low pressure of approximately 12 mm Hg will adjust in thespace 16, with which a temperature of [.8 "K is associated, so atemperature lower than that of the itpoint of helium. This means thatthe helium in the heatexchanger 18 will also assume this lowtemperature. Since a differential pressure prevails across the seriesarrangement of superfluid will start flowing through the superleak 19 tothe space 20 while superfluid and normal helium flow to the space 16through the vortex tube I 21 in which the superfluid exceeds itscritical velocity. Since with the superfluid no thermal energy istransported through the superleak to.the space 20, while with the flowof normalfluid through the vortex tube thermal energy is indeed removedfrom the space 20, the space 20 will show alower temperature, forexample, in the order of K, than the heat exchanging space 16. In thismanner a device is obtained with which cold is produced at very lowtemperatures, while the suction pressure of the compression device 1nevertheless need be only 1 atmosphere.

The cold produced in the space can be used for cooling articles, forexample, electric components, infrared cells superconductive resonantcavities, and so on. These articles may be, for example, in directcontact with the space 20. However, for all kinds of structural reasonsa certain distance will usually exist between the space 20 and thearticle to be cooled, certainly when cooling of several articles whichare arranged at a distance from each other have to be cooled with onespace 20. This cooling at a distance can very efflciently be carried outby communicating a duct 23 at its one side with the space 20 andbringing its other side in thermal contact with an article 27 to becooled. So helium at a temperature below that of the )t-point of heliumwill also be present in the duct 23. It is known that this helium at thesaid temperatures has an extremely good thermally conductive power whichmay be up to l,000 times higher than that of solid substances. Thisproperty can be explained by the fact that at said temperatures thehelium consists partly of normal fluid, with viscosity and entropy, andpartly of superfluid which shows no viscosity and entropy. When atemperature difference is applied between two places in the said helium,the superfluid will flow to the place with the higher temperaturewithout transporting thermal energy, while normal fluid flows in theopposite direction in such manner that the overall mass flow is zero.With this normal fluid thermal energy is transported indeed. It has beenfound that the mutual friction between normal and superfluid by movingvortices in the superfluid adversely influences the thermal conductivityof Hell.

In the device shown in FIG. 1 this disadvantageous effect has beencounteracted by covering the inner wall of the duct 23 with a superleak24 of, for example, aluminum oxide particles of silicon carbideparticles of very small dimensions which are sintered together. Such asuperleak has the property that normal fluid cannot pass it whilesuperfluid flows through it without moving vortices occurring. Whenthermal energy is supplied to the end 28 of the duct 23 by the articleto be cooled, said end 28 will assume a slightly higher temperature thanthat prevailing in the space 20. A differential pressure corresponds tothis temperature difference across the duct 23, so that normal andsuperfluid flows through the core of the duct 23 to the space 15, whilean equally large mass flow of superfluid flows through the superleak 24to the article 27 to be cooled. With the flow of normal fluid thermalenergy of the article to be cooled is transported to the space 20, thetransported heat flow being proportional to the rate of flow of thenormal fluid. Since no mutual friction is present between the flow ofnormal fluid and the flow of superfluid in the direction of the end 28of the duct (superfluid flows through the superleak), the temperaturegradient across the duct is not adversely influenced thereby so that alarge heat flow from the article to be cooled to the space 20 isobtained with a small temperature difference between the article to becooled and the space 20.

It is not necessary for the superleak 24 to be arranged against theinner wall, although this does provide the advantage that heat leak fromwithout is counteracted; however, it is alternatively readily possibleto arrange the superleak 24 detached from the wall of the tube, forexample, as a core in the duct.

Instead of contacting the end 28 of the duct with an article 27, theduct 23 may communicate with its end 28 with a further space whichserves either as a cold buffer for the article to be cooled, or as aspace from which liquid can be drained.

FIG. 2 shows a device which in general is equal to the device shown inFIG. 1, but in which the superleak l9 communicates with the place 30 ofthe system of supply ducts, via the heat exchanger 18 and throttle valve15 a further heat exchanger 13. A throttle valve 31, in which thehigh-pressure helium expands from 30 atm. to, for example, 5 atm, isaccommodated in the system of supply ducts. It is to be noted that sucha throttle valve is not strictly necessary and may be dispensed with incircumstances. In the device shown in FIG. 1, said throttle valve 31 mayalso be present. The operation of this device is the same as that shownin FIG. 1. High-pressure helium is supplied both to the ejector 9 and tothe throttle valve 15. In the heat exchanger 18, again a temperaturewill prevail which is lower than that of the k-point of helium, so thatin combination with the differential pressure across the seriesarrangement of superleak 19, cold space 20 and vortex tube 21, cold willagain be produced in the space 20 at a very low temperature.

It is shown in FIG. 3 how the heat-exchanging store 16 can have the formof a real heat-exchanger. For the rest, this device is quite similar tothat shown in FIG. 2.

FIG. 4 shows a device for producing cold at very low temperatures whichin general also corresponds to the device which is shown in thepreceding Figures, but in which the high-pressure helium is firstexpanded in the throttle valve 31 to, for example, a pressure of 5atmosphere, after which this expanded helium is further expanded in asecond throttle valve 32 to, for example, a pressure of 17 mm Hg, whichpressure therefore also prevails in the heat exchanging space 33. Theinlet side of the superleak l9 communicates with a place 34 which,viewed in the direction of flow, is situated in front of this throttlevalve 32, while the vortex tube 21 communicates with the store 33,Between the place 34 and the superleak a throttle valve 15 is againprovided and a heat exchanger 18 in which a temperature prevails whichlies below that of the )t-point of helium, while the pressure there ishigher than in the space 33, so that again superfluid helium will startflowing through the superleak 19 without moving vortices occurring andfrom the store 20 helium will flow through the vortex tube 21, in whichthe superfluid helium exceeds its critical velocity, to the space 33 andthen through the system of outlet ducts 11 to the inlet side of thecompression device 1. In this device also the production of cold in thespace 20 will occur at a temperature which is lower than that in thespace 33, in which the compression device 1 needs sucking only at apressure which corresponds to the pressure in the space 33.

It will be obvious from the above that the invention provides anextremely simple extension of a Joule-Kelvin system with which it ispossible, without the introduction of moving components and without thepresence of an extremely bulky compression device, to produce cold attemperatures in the proximity of lK and lower. Devices or the type towhich the present invention relates are therefore suitable for use asprecoolers for He-l-le mixture refrigerators, with which it is possibleto produce cold continuously at temperatures in the proximity of 20millidegrees K.

What is claimed is:

l. A device for producing cold at temperatures lower than that of the)t-point of helium, which device in cludes a source for high-pressurehelium with a low pressure suction inlet, and a high pressure outletwhich communicates with a supply duct system including at least onepre-cooler and at least one counter-current heat exchanger in which thehigh-pressure helium is cooled to below its inversion temperatureassociated with the said pressure, the counter-current heat exchangercommunicating with at least one throttle device in which thehigh-pressure helium expands to a second lower pressure, the expandedhelium then flowing, via an outlet duct system and said counter-currentheat exchanger to said suction side of said source, characterized inthat the device furthermore comprises a further heat exchanger, a coldspace, a throttle valve, a vortex tube, and at least one superleak whichcommunicates on its one side via said further heat exchanger in whichthe helium cools to below the x-temperature of helium and said throttlevalve with said outlet duct system, and communicates on its other sidewith said cold space, said cold space furthermore communicating via saidvortex tube, with said He at said second lower pressure which is a lowerpressure than prevails at said cold space.

2. A device as claimed in claim 1, characterized in that said throttledevice is formed by a throttle ejector, the outlet of said ejectorcommunicating on one side with the system of outlet ducts and on theother side via a counter-current heat exchanger and a throttle valve,with a heat exchanging space the vapor space of which communicates, viasaid counter-current heat exchanger, with the suction side of theejector, the superleak communicating with its one side via aheatexchanger, in which the helium exchanges heat with the heatexchanging space, a throttle valve and a further heat exchanger, with afirst place of the system of supply ducts situated before the throttleejector in the direction of flow, the vortex tube communicating with theheat exchanging space.

3. A device as claimed in claim 1, characterized in thatat least one ofthe said throttle devices is formed by a throttle ejector, the outlet ofsaid ejector communicating on the one side with the system of outletducts and communicating on the other side, via a countercurrent heatexchanger and a first throttle valve, with a heatexchanging space thevapor space of which communicates, via the counter currentheat-exchanger, with the suction side of the ejector, the superleakcommunicating with its one side, via a heat-exchanger in which thehelium exchanges heat with the heatexc hanging space, and a secondthrottle valve, with a place between the first throttle valve and theheatexchanger, the vortex tube furthermore communicating with theheat-exchanging space.

4. A device as claimed in claim 1, further comprising a further space,and further duct means having one end communicating with said coldspace, and a remote end thermally contactable with said further space,said further duct means comprising a sintered superleak.

which extends throughout the length of the duct and covers a part ofthecross-section thereof.

5. A device as claimed in claim 4, characterized in that the superleakcovers the entire inner wall of the further duct.

6. A cryogenic refrigerator apparatus for producing cold at atemperature lower than the )t-point of helium, comprising a source of Hegas with a first high pressure and a first high temperature, a supplyduct means for transporting He from said source, first meansfor coolingHe in said supply duct means to a second tempera-. ture below theinversion temperature associated with said first pressure, second meansfor expanding the cooled He from said first means to a second lowerpressure, further duct means for dividing said expanded He from saidsecond means into first and second portions, third means for furtherexpanding and cooling said second portion of He to a third temperaturebelow the )t-point thereof and for forming at least some of said secondportion He into superfluid He and the remainder of said second portioninto normal liquid He, a cold space container, a superleak communicatingbetween said third means and said cold space container, a vortex tubecommunicating between said cold space container and said third means,whereby the superleak permits passage of only superfluid He from saidthird means to said cold space container, and a turbulent flow of normaland superfluid He occurs in the vortex tube from said container to saidthird means.

7. Apparatus according to claim 6 wherein said first means for coolingHe comprises heat exchangers, said second means comprises an ejector,said third means comprises a Joule-Thompson throttle expander andfurther heat exchanger, and said vortex tube has an aperture with across-section corresponding to the pressure differential across saidaperture such that the flow of normal He therethrough is turbulent.

8. Apparatus according to claim 6 wherein said second means comprises athrottle-device for expanding said He.

9. Apparatus according to claim 6 further comprising a second containerfor containing liquid He formed by said third means, and means forapplying low pressure suction on said second container from said secondmeans.

10. Apparatus according to claim 6 wherein said third means comprises athrottle device.

11. Apparatus according to claim 6 wherein said second means is anejector including an inlet, an outlet, and a suction side, the apparatusfurther comprising a heat exchange container having space for liquid andvapor He from said third means,,return duct means communicating saidvapor to the suction side of said ejector, said return duct means beinga counter-flow portion of a heat exchanger for cooling said secondportion of said He before it is expanded by said third means.

12. Apparatus according to claim 11 furthercomprising final heatexchange means being cooled by said liquid He in said heat exchangecontainer, the apparatus further comprising fourth means for furtherexpanding He from said ejector and communicating this expanded He tosaid final heat exchanger with the superfluid He thereformedcommunicated to said superleak.

13. Apparatus according to claim 11 further comprising final heatexchange means being cooled by said liquid He in said, heat exchangecontainer, the apparatus further comprising fourth means for furtherexpanding some of the He from said first means, and communicating thisexpanded He to said final heat exchanger with the superfluid Hethereformed communicated to said super-leak.

14. Apparatus according to claim 11 wherein said second means is athrottle device, said third means comprises a throttle device receivingHe from said further duct means and expanding said He and communicatingsame to be cooled in a counterflow heat exchanger with the superfluid Hethereformed then communicated to said superleak, said counterflow heatexchanger cooled by He from said vortex tube which is then communicatedto said suction side of the ejector.

15. Refrigeration apparatus comprising a source of He at a first highpressure and an inlet for receiving He at a second lower pressure,supply duct means for transporting said high pressure He from saidsource,

return duct means for transporting He to said source inlet, first meansfor cooling He in said supply duct means to below the inversiontemperature associated with said first pressure, second means forexpanding and further cooling He from said supply duct means anddividing same into first and second portions, third means for furtherexpanding said first portion and for further cooling same to below the)t-point thereof to form a mixture of normal and superfluid He, a coldspace container, a superleak which permits passage of only superfluid Hefrom said third means to said cold space container, a vortex tubethrough which flows both normal and superfluid He from said container tosaid second means, and means for communicating said second portion ofexpanded He to said return duct means. I

i l l t! t

1. A device for producing cold at temperatures lower than that of thelambda -point of helium, which device includes a source forhigh-pressure helium with a low pressure suction inlet, and a highpressure outlet which communicates with a supply duct system includingat least one pre-cooler and at least one counter-current heat exchangerin which the high-pressure helium is cooled to below its inversiontemperature associated with the said pressure, the counter-current heatexchanger communicating with at least one throttle device in which thehigh-pressure helium expands to a second lower pressure, the expandedhelium then flowing, via an outlet duct system and said counter-currentheat exchanger to said suction side of said source, characterized inthat the device furthermore comprises a further heat exchanger, a coldspace, a throttle valve, a vortex tube, and at least one superleak whichcommunicates on its one side via said further heat exchanger in whichthe helium cools to below the lambda -temperature of helium and saidthrottle valve with said outlet duct system, and communicates on itsother side with said cold space, said cold space furthermorecommunicating via said vortex tube, with said He at said second lowerpressure which is a lower pressure than prevails at said cold space. 2.A device as claimed in claim 1, characterized in that said throttledevice is formed by a throttle ejector, the outlet of said ejectorcommunicating on one side with the system of outlet ducts and on theother side via a counter-current heat exchanger and a throttle valve,with a heat exchanging space the vapor space of which communicates, viasaid counter-current heat exchanger, with the suction side of theejector, the superleak communicating with its one side via aheat-exchanger, in which the helium exchanges heat with the heatexchanging space, a throttle valve and a further heat exchanger, with afirst place of the system of supply ducts situated before the throttleejector in the direction of flow, the vortex tube communicating with theheat exchanging space.
 3. A device as claimed in claim 1, characterizedin that at least one of the said throttle devices is formed by athrottle ejector, the outlet of said ejector communicating on the oneside with the system of outlet ducts and communicating on the otherside, via a counter-current heat exchanger and a first throttle valve,with a heat exchanging space the vapor space of which communicates, viathe counter curRent heat-exchanger, with the suction side of theejector, the superleak communicating with its one side, via aheat-exchanger in which the helium exchanges heat with theheat-exchanging space, and a second throttle valve, with a place betweenthe first throttle valve and the heat-exchanger, the vortex tubefurthermore communicating with the heat-exchanging space.
 4. A device asclaimed in claim 1, further comprising a further space, and further ductmeans having one end communicating with said cold space, and a remoteend thermally contactable with said further space, said further ductmeans comprising a sintered superleak which extends throughout thelength of the duct and covers a part of the cross-section thereof.
 5. Adevice as claimed in claim 4, characterized in that the superleak coversthe entire inner wall of the further duct.
 6. A cryogenic refrigeratorapparatus for producing cold at a temperature lower than the lambda-point of helium, comprising a source of He gas with a first highpressure and a first high temperature, a supply duct means fortransporting He from said source, first means for cooling He in saidsupply duct means to a second temperature below the inversiontemperature associated with said first pressure, second means forexpanding the cooled He from said first means to a second lowerpressure, further duct means for dividing said expanded He from saidsecond means into first and second portions, third means for furtherexpanding and cooling said second portion of He to a third temperaturebelow the lambda -point thereof and for forming at least some of saidsecond portion He into superfluid He4 and the remainder of said secondportion into normal liquid He4, a cold space container, a superleakcommunicating between said third means and said cold space container, avortex tube communicating between said cold space container and saidthird means, whereby the superleak permits passage of only superfluidHe4 from said third means to said cold space container, and a turbulentflow of normal and superfluid He4 occurs in the vortex tube from saidcontainer to said third means.
 7. Apparatus according to claim 6 whereinsaid first means for cooling He comprises heat exchangers, said secondmeans comprises an ejector, said third means comprises a Joule-Thompsonthrottle expander and further heat exchanger, and said vortex tube hasan aperture with a cross-section corresponding to the pressuredifferential across said aperture such that the flow of normal He4therethrough is turbulent.
 8. Apparatus according to claim 6 whereinsaid second means comprises a throttle device for expanding said He. 9.Apparatus according to claim 6 further comprising a second container forcontaining liquid He formed by said third means, and means for applyinglow pressure suction on said second container from said second means.10. Apparatus according to claim 6 wherein said third means comprises athrottle device.
 11. Apparatus according to claim 6 wherein said secondmeans is an ejector including an inlet, an outlet, and a suction side,the apparatus further comprising a heat exchange container having spacefor liquid and vapor He from said third means, return duct meanscommunicating said vapor to the suction side of said ejector, saidreturn duct means being a counter-flow portion of a heat exchanger forcooling said second portion of said He before it is expanded by saidthird means.
 12. Apparatus according to claim 11 further comprisingfinal heat exchange means being cooled by said liquid He in said heatexchange container, the apparatus further comprising fourth means forfurther expanding He from said ejector and communicating this expandedHe to said final heat exchanger with the superfluid He4 thereformedcommunicated to said superleak.
 13. Apparatus according to claim 11further comprising final heat exchange means being cooled by said liquidHe in saiD heat exchange container, the apparatus further comprisingfourth means for further expanding some of the He from said first means,and communicating this expanded He to said final heat exchanger with thesuperfluid He4 thereformed communicated to said superleak.
 14. Apparatusaccording to claim 11 wherein said second means is a throttle device,said third means comprises a throttle device receiving He from saidfurther duct means and expanding said He and communicating same to becooled in a counterflow heat exchanger with the superfluid He4thereformed then communicated to said superleak, said counterflow heatexchanger cooled by He from said vortex tube which is then communicatedto said suction side of the ejector.